1. Field of the Invention
This invention relates generally to hearing protective earplugs and is more specifically directed to a selective nonlinear attenuating earplug construction useful as a hearing protector.
2. Brief Discussion of the Prior Art
Environmental sounds are typically comprised of a mixture of various sound wave frequencies having varying intensities. It is well documented that repeated or prolonged exposure to sounds of sufficiently high sound pressure level will cause temporary or permanent hearing loss. For example, exposure to sound waves of some frequencies and of varying intensities under conditions of severe impact can damage the auditory organ and cause serious hearing problems, including deafness. Injurious noises such as those caused by explosions or bursts are often comprised of a mixture of sound wave frequencies of varying intensity. These disturbing frequencies are in both the high and low frequency bands and have an intensity sufficient to cause hearing problems. Individuals who are frequently exposed to sound having such disturbing and sometimes dangerous frequencies and intensities run the risk of incurring such injuries as hearing loss or even deafness. These individuals include workers at demolition or construction sites, operators of heavy, noisy equipment and those in active military service. Ear (i.e. hearing) protection is needed to prevent a loss in hearing acuity and the gradual increase in the threshold of hearing resulting from extended exposures to loud noise.
Sound attenuation devices are known which specifically address this problem. These include conventional earplugs, earmuffs, and the like which function to reduce the negative effects of exposure to dangerous frequencies by limiting the entry of all sound waves into the auditory organ. Sound attenuation devices may be either linear or nonlinear in nature. Linear attenuation devices attenuate sound at a predetermined level regardless of the frequency of the sound, while nonlinear devices attenuate sound at different levels have depending upon the frequency of the sound. These conventional devices suffer from a significant disadvantage, namely that auditory access to environmental sounds of relatively risk free frequencies is also limited. Thus, the devices suffer from the limitation that they provide much greater attenuation at high frequencies than at low frequencies and/or provide excessive attenuation at high frequencies. The result is that the wearer of these devices who wanted or needed to hear clearly was prevented from doing so. Therefore, while these devices were protective to some extent against the effects of overexposure to sound having dangerous frequencies and intensities, they in themselves created a new danger in that they shut out all environmental sounds including those of speech and warning.
Devices designed to increase the audibility of earplugs are known in the art. For example, in U.S. Pat. No. 4,540,063 to Ochi et al., there is disclosed an earplug construction capable of attenuating sound waves of multiple frequencies. The earplug comprises an outer shell having inlet and outlet apertures at opposite ends and containing a sound wave attenuation unit disposed between the apertures such that environmental sound waves enter the earplug through the inlet aperture, penetrate the sound wave attenuating unit wherein sound waves are attenuated and exit the earplug through the outlet aperture. The sound wave attenuating unit is composed of a first and a second plate of a sound absorbing material positioned near the inlet and outlet apertures respectively and a pair of thin sheets of a fabric having substantially uniform air permeability and elasticity disposed therebetween and forming an air chamber between the sheets.
In U.S. Pat. No. 5,113,967 to Killion et al., there is disclosed an earplug construction for improved audibility. The earplug comprises an eartip portion arranged for positioning with at least an inner end portion thereof in an ear canal to define a first sound passage extending from an inner end within the ear canal to an opposite outer end, and in which a second sound passage is formed by a structure which is preferably external to the ear canal, the second sound passage having an inner end coupled to the outer end of the first passage and having an opposite sound-receiving outer end. An important feature is that the second passage includes a portion folded back on itself. Through the use of an earplug construction in which an assembly contains an acoustic damper between two sound channels, the first being the sound tube internal to the eartip and the second being external folded back portion, the attenuation of sound waves is realized.
By providing a selective attenuation mode, the earplug can offer the wearer the ability to choose between two different performance settings for the earplug depending upon the exact environment in which the wearer intends to use the earplugs. In the selective mode, sound attenuation is low for a specific range of intensities above those in the specified range. Selective attenuation is especially effective for the loudest noises. A sample application of the earplug in the selective attenuation mode is the intelligible speech transmission in a noisy environment caused by pulsed noises, such as gunshots, for example. In the maximum attenuation mode, the earplug stops all sounds throughout the intensity range, regardless of their intensity.
While suitable for their intended purpose, there is a perceived need for a more effective and improved earplug device whereby the earplug offers different levels of attenuation and is sized to fit most ears. The selective attenuation earplug devices of the prior art suffer from the disadvantage that these earplugs are not particularly well suited for environments where selective attenuation and maximum attenuation is desired and the capability of easily and quickly interchanging the device from one mode to another is desired.